Galactooligosaccharide (GOS) is a functional oligosaccharide that is currently widely used in the food industry. As a new functional food additive, the GOS has attracted worldwide attention because of its unique physiological functions and excellent physicochemical properties. With the continuous advancing of development and research of GOS, coupled with abundant raw materials in China and the unlimited potential of the consumer market, the production of GOS has already set off a strong momentum all over the country. At present, the production of oligosaccharides in China is still an emerging industry. The development of GOS has not yet reached its scale. The main reason for restricting the production of GOS in China is the lack of industrial enzymes with excellent performance. Therefore, it is very important to find industrial enzymes with excellent performance.
β-galactosidase is a main enzyme used in industrial enzymatic method production of galactooligosaccharide. β-galactosidase derived from different microorganisms has different ability to generate GOS due to different properties. Currently known better GOS-producing strains are B. circulans, Kluyveromyces Lactis and A. oryzae. Although the yield of B. circulans (Bacillus circulans) is higher (48.3%), its product of GOS production is mainly 4′GalLac which has a poor probiotic effect. A main product of GOS produced by A. oryzae as a food-safe strain is 6′GalLac. 6′GalLac has a better probiotic effect than 4′GalLac, but its yield is only about 19%, which greatly limits its application.
Therefore, improving the yield of Aspergillus oryzae derived β-galactosidase for producing GOS to create conditions for its industrial production is a technical problem to be solved at present.